@rotorfido You should change the post title to something more accurate. It is absolutely spurious. I could make some suggestions as to more accurate post titles but many of the community guidelines would be broken as to obscenity and respectful conduct.
A quick examination of your mail-tester.com link
https://www.mail-tester.com/test-mq9qa8imx
And 2 minutes on Google provided the answer
It doesn’t appear to be dangerous per se, but it allows a particularly formatted message from the
postMessageAPI to cause thenavigator.geolocationAPI to output garbage, if enabled, probably as part of an extension you’ve installed to browse “anonymously”.
And
This is caused by having the ExpressVPN plugin enabled - uninstall the browser plugin, and it’ll go
It appears to be a browser extension you use is causing this and probably most of the rest of the problems you have been having that you posted about